Magnetics Business & Technology - July/August 2024 - 18

RESEARCH & DEVELOPMENT
A Blueprint for More Powerful Superconducting Magnets
these cables become superconducting.
These magnets, known as high-temperature superconducting
(HTS) magnets, have the potential to generate magnetic fields
greater than 100 T and at higher temperatures than LTS magnets.
This reduces their reliance on liquid helium, making them much
more cost-effective to operate than LTS magnets.
While HTS magnets promise very high magnetic fields, how to
turn them into a superconducting accelerator magnet, says Shen,
" remains a critical question. "
Tengming Shen (left) and Laura Garcia Fajardo working on the new HTS
magnet design at the Superconducting magnet fabrication lab in the
Accelerator Technology & Applied Physics Division at Lawrence Berkeley
National Laboratory (Credit: Berkeley Lab)
Researchers from the Accelerator Technology & Applied Physics
(ATAP) Division at Berkeley Lab, in collaboration with colleagues
from the Lab's Engineering Division and the Applied Superconductivity
Center at the National High Magnetic Field Laboratory
(NHMFL), have built a new superconducting magnet that shows potential
for generating extremely high magnetic fields. It could enable
more powerful, energy-efficient particle accelerators that are less
expensive to build and operate than current technologies, leading to
breakthroughs in high-energy physics and fusion research and enhancing
the capabilities of magnetic resonance imaging machines
used in medical diagnosis.
Superconducting magnets are essential components of accelerators
as they guide the trajectory of the charged particles and determine
the accelerator's energy reach. The highest field magnets
installed in an accelerator are those in the Large Hadron Collider
(LHC) at CERN. These magnets are made from niobium-titanium
(Nb-Ti), which are capable of producing magnetic fields of about
8 T. The High Luminosity Large Hadron Collider (HL-LHC) project
aims to upgrade the LHC with magnets made from niobium-tin
(Nb3Sn), which can produce fields as high as 11 T.
Nb-Ti and Nb3Sn are low-temperature superconductors (LTS);
magnets made from these conductors are operated at liquid helium
(the refrigerant used to cool the magnets) temperatures of 1.9 to 4.2
K.
" Although magnets made of Nb3Sn have the potential to generate
magnetic fields of up to about 16 T, " says Tengming Shen, a Staff
Scientist at ATAP's Superconducting Magnet Program who led
the development of the new magnet, " extending the energy reach
of future accelerators will require increasingly powerful magnets,
capable of generating very high magnetic fields of 20 T or more. "
While such magnets would enable new areas of research in particle
physics, fusion, and medicine, Shen says magnetic fields of this
magnitude " are beyond the capabilities of LTS magnets. "
To create more powerful magnets, the researchers turned to novel
magnet designs that use superconducting cables made from new
materials with high critical temperatures-the temperature at which
18 Magnetics Business & Technology * July/August 2024
Schematic of a canted-cosine-theta (CCT) dipole magnet with a crosssectional
cut that shows a cosine-theta-like current distribution that
delivers the excellent field quality required by a high-energy physics
accelerator magnet. (Credit: Berkeley Lab
The new magnet is based on a canted-cosine theta design (CCT),
which can generate uniform, high-strength magnetic fields. And was
constructed using superconducting cables made from a bismuthstrontium-calcium-copper
oxide compound-a promising new material
for making superconducting cables. Commonly referred to as
Bi-2212, it is the only multifilamentary round wire HTS available in
long lengths and capable of delivering high critical current density
and small magnetization, which are crucial for achieving high field
quality.
According to Shen, the magnet " is the world's first HTS dipole magnet
that combines the CCT design with Bi-2212 superconducting
cables. It could enable two frontiers; a high-magnetic field frontier
and a high-temperature frontier, allowing it to operate at a higher
temperature and thereby reducing its reliance on liquid helium,
which is expensive and supplies are running low. "
The CCT design also has the advantage of stress management
capabilities, which he says are essential because the stress and
forces on the magnet increase with the square of the magnetic field.
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" For instance, these magnets must be easy to fabricate and capable
of maintaining the high critical current density in the strong magnetic
fields generated by the superconducting cables. They must
also meet several other requirements, including the ability to handle
large electromagnetic forces while delivering high magnetic field
quality. "
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Magnetics Business & Technology - July/August 2024

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